Talk Contact

AAAI Talk Contacts

Welcome to the personal site of Houjun “Jack” Liu.

I’m on the blaggosphere as u/jemoka and @jemoka.

Who’s this guy?

I am a human interested in linguistic analysis, NLP, and user interfaces. I think AGI & Emacs are cool. I run Shabang, do research in NLP and model-based RL, and am working for TalkBank on the intersection between speech and language.

I’m currently doing my undergrad at Stanford, where I write some code for Stanza, a NLP package for many human languages, and a rover that we are sending to Antarctica.

Here’s a fun implementation of absolute value.

long abs_value(long num) {
    long sign = num >> (sizeof(long)*CHAR_BIT - 1); // so you only get all 1s or all 0s

    return (num ^ sign) - sign; // sign is either -1 or 0. So, if num is non-negative
                                // num^sign is not going to do anything (as 0^0 = 0, 0^1 = 1).
                                // If num negative, num^sign is going to flip the bit AND subtract
                                // negative on (i.e. add one)
}

abstract syntax tree is what happens when CFGs is applied to text (i.e., the parser traces the AST in time).

Building an AST

Generally, each production will have an action, which is the relevant computation.

X -> Y1... Yn { action }

Each symbol X admits an attribute X.val

• for each terminal, val is the associated lexeme
• for non-terminals, val is the expression’s value (i.e., from the values of the subexpressions)

you job is to compose the subexpressions’ values and stick it into X.val. Notably, cycles are not allowed because we typically parse bottom-up, left ot right.